@rjehangir Hello, I am having this same problem.
I am using the Fathom-X Topside Interface (FXTI) for BlueROV2 and a USB cable to connect it to my PC. On the ROV side the Fathom-X Tether Interface rev2 is wired as it comes with the BlueROV2 Electronics Enclosure.
On both sides both Link Active and Power LEDs are flat green (not blinking) when I try: ping 192.168.2.2 the host cannot be reached, but when I connect the Raspberry through an Ethernet cable everything works fine.
One thing to notice is that everything has been working fine since the first dive and today when I tried to power up everything as usual it stopped working.
Do you have any idea what can be wrong? Is there any way to troubleshoot the Fathom X board alone?